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As the title says, I'm restoring an original 1990 Fatboy that has 17k miles on it. Before I tore it all apart, I rode for about 10 minutes when I was delivered to my house from PA. It ran strong and there was no smoking or any abnormal sounds. The bike had been sitting for a bit. I want to go through the engine to make sure there are no leaks when everything is back together. Check my logic/sanity below.
Planning to order the Cometic top end gasket kit. I've always been partial to Cometic when building Twin Cams. The engine is stock so I'm thinking of the kit with the .040 head gaskets. https://www.cometic.com/products/C9747
Pull the rockers, heads, and cylinders. I was thinking MAYBE hone the cylinders and re-ringing it but it only has 17k miles. I'll make that decision when I pull the heads and look at the cylinders. Thoughts? Going through the heads as well with new seals, cleaning, etc.
Since I'm restoring back to original, I don't want to do any engine work to increase HP/TQ. It will have stock exhaust (maybe some slip-ons) but it will have the stock air box. It has a Baker 6 speed OD and I'm going to replace it with a stock 5 speed and sell the Baker. Even though I plan to ride it when it's finished, I don't need OD and I want it original.
Splitting the cases? I've done it on a few Twin Cams but never an Evo, but it can't be much different. I'm extremely well verse with engine work. I'm thinking that I should split the cases since the bike is 35 years old and make sure it's good for another 35 years. What do the Evo experts think?
Please jump in with anything else I haven't thought of doing.
If your tearing things apart, then correct some things that MoCo had no choice (epa mandates) or cheaped out on.
Why not add a mild cam and bump compression just a tad (very slight). This will make the bike run better, more efficient, and not affect durability at all. At least go with .030 head gasket. I think stock thickness is .045 Improve the way it runs and get some benefit of a little more "pep" and mileage gains as well.
May I suggest:
You have the "L" cam so better than the EPA mandated "N" cam, but an aftermarket "mild" cam will still be an improvement if you select the correct one and will not hurt a thing, it can only help how your bike runs and feels.
You still have the torrington full compliment cam bearing, so that is a plus, but if you swap the cam, then maybe change the bearing. Later models had a cheaper cam bearing with some failures.
Consider a better ignition with a better (better than stock) advance curve also.
Never been in a Harley bottom end so I will defer to others, but there is no need to go into the bottom end. Hell there is no need to do a top end but you already have the engine pulled. Your a bottom breather so no dried up umbrella valves to worry about.
I say leave it alone and run it/ride it if your not going to do any upgrades. If it was a good runner, leave it alone and wait till you get some miles on it. You may change your mind about upgrades later on.
Evo’s could have have some lifter issues at about 25k miles, it’s apart so I would change them, that and adjustable push rods just in case you change your mind on on the Cam, a mild bolt in ev27 will give it just a little snap and is era correct with the adjustables it’s not such a chore changing the cam or any maintenance going forward.
You really shouldn’t see a need to crack the cases, it’s pretty robust. @Yankee Dog is correct on changing the ignition, it will also give you better curve and adjustability that even with the cam is not seen or known by anyone but you.
If your tearing things apart, then correct some things that MoCo had no choice (epa mandates) or cheaped out on.
Why not add a mild cam and bump compression just a tad (very slight). This will make the bike run better, more efficient, and not affect durability at all. At least go with .030 head gasket. I think stock thickness is .045 Improve the way it runs and get some benefit of a little more "pep" and mileage gains as well.
May I suggest:
You have the "L" cam so better than the EPA mandated "N" cam, but an aftermarket "mild" cam will still be an improvement if you select the correct one and will not hurt a thing, it can only help how your bike runs and feels.
You still have the torrington full compliment cam bearing, so that is a plus, but if you swap the cam, then maybe change the bearing. Later models had a cheaper cam bearing with some failures.
Consider a better ignition with a better (better than stock) advance curve also.
Never been in a Harley bottom end so I will defer to others, but there is no need to go into the bottom end. Hell there is no need to do a top end but you already have the engine pulled. Your a bottom breather so no dried up umbrella valves to worry about.
I say leave it alone and run it/ride it if your not going to do any upgrades. If it was a good runner, leave it alone and wait till you get some miles on it. You may change your mind about upgrades later on.
Originally Posted by Paintslinger16
Evos could have have some lifter issues at about 25k miles, its apart so I would change them, that and adjustable push rods just in case you change your mind on on the Cam, a mild bolt in ev27 will give it just a little snap and is era correct with the adjustables its not such a chore changing the cam or any maintenance going forward.
You really shouldnt see a need to crack the cases, its pretty robust. @Yankee Dog is correct on changing the ignition, it will also give you better curve and adjustability that even with the cam is not seen or known by anyone but you.
Thanks for the feedback! I talked to the guy that sold me the bike. He was a friend of the original owner who passed away and helped sell the bike for his estate. He said the bike has a Scream'n Eagle Cam already. It has Scream'n Eagle ignition as well, but I think it has the stock module in the timing cover because the rivets are still in the timing cover. I will probably keep those in the bike. I want to see which SE cam it has because I believe they had 3 different cams. I was thinking of an Andrews EV27. I had one in my FXR4 and it gave the bike some pep.
If the bike didn't have historical significance, I would make a lot of modifications. But as the first year Fatboy (Grey Ghost), they are very sought after in stock form. The original owner had a ton of chrome parts that I'm removing and going back to stock. Example are the floorboard mounts which are chrome and they were black from the MoCo.
The EV 27 was a pretty common upgrade I actually would not be surprised if it’s in there all ready.
Do you have a Fatboy AC cover or the SE? I have been looking for a Low rider one they don’t pop up very often.
someone here on the forum did have a replacement SE cover so I was able to refresh it some etching had got under the clear coat.
I'd change the breather gear from plastic to steel. The plastic teeth get brittle and break off with age. You can check what cam you have while you're in there.
On my older bikes I add 1/2 bottle of STP High Milage oil treatment at each oil change. It contains seal conditioners. Good for valve guide seals, rubber gaskets and O'rings.
Splitting the cases? I've done it on a few Twin Cams but never an Evo, but it can't be much different. I'm extremely well verse with engine work. I'm thinking that I should split the cases since the bike is 35 years old
Just ride it.
Last edited by Dan89FLSTC; May 21, 2025 at 06:24 PM.
No need to tear it down especially the cases. That motor is barely broken in.. If you want to do anything, valve seals and a .030 head gasket with new base gaskets.. anything more than that and you're probably throwing your money away..
Keeping with the stock cam position sensor was normal when upgrading to the Screamin Eagle ignition module. They work very well and were made by Dynatek, some model ignition modules even had selectable ignition curves..
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1990 Fatboy Restoration - Engine reseal
